- [ Home ](/) / - Compatibility matrix # Compatibility matrix A claim of support needs a source and a scope. This matrix separates what a publisher can implement from what a client has documented or what a dated observation has measured. Last updated: August 12, 2026 ## Evidence classes Capability What can be verified What it does not prove /llms.txt publication HTTP response, content type and file syntax can be checked live. Automatic client discovery or impact on an AI answer. Markdown alternate A page can expose rel="alternate" type="text/markdown" . That any named tool fetches it. describedby The relation can be present in HTML or an HTTP Link header. Universal v2 support or a ranking signal. Client behavior Provider documentation or a reproducible, scoped test. Behavior of another client or a future version. ## Current observatory baseline In the current fixed-panel discovery observation, 28 pages exposed a Markdown alternate and 4 exposed `describedby`. This is a publication baseline, not a client leaderboard. The raw figures and limits are in the [Observatory](/observatory/). ## How to use the matrix - Implement a capability you can maintain and verify. - Link to the source that describes any client claim. - Use *unknown* when neither a source nor a reproducible observation exists. - Recheck claims after a product or specification release. ## Sources - [ llmstxt.org, v2 proposal ](https://llmstxt.org/)